DRIVING METHOD OF A DISPLAY DEVICE AND DISPLAY DEVICE
A driving method of a display device includes: supplying a first drive voltage from a first circuit, which is driven using a first power-supply voltage from a first power source, and a second drive voltage from a second circuit, which is driven using a second power-supply voltage from a second power source that is lower than the first power-supply voltage; causing a driver circuit section that drives a display element to charge, using the second drive voltage, a display element in a non-selected region in a display element section that includes a plurality of display elements; maintaining a voltage of the display element in the non-selected region, using the second drive voltage.
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This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2009-287961, filed on Dec. 18, 2009, the entire contents of which are incorporated herein by reference.
FIELDThe present invention relates to a driving method of a display device and a display device.
BACKGROUNDIn recent years, the development of a display device called rewritable electronic paper or the like has been promoted in which display content can be maintained even if the display device is powered off. One display method performed in the electronic paper is a display method that utilizes a liquid-crystal composition in which a cholesteric phase is formed. Examples of the liquid-crystal composition in which a cholesteric phase is formed include cholesteric liquid crystals. The cholesteric liquid crystals are also referred to as chiral nematic liquid crystals. The cholesteric liquid crystals form a cholesteric phase in which molecules of the nematic liquid crystal are in the form of a helix by adding a chiral additive into a nematic liquid crystal. The cholesteric liquid crystals have excellent characteristics, such as a semi-permanent display maintaining function (memory function), a vivid color display characteristic, a high contrast ratio, and a high resolution characteristic.
A display device that utilizes the cholesteric liquid crystals performs multi-color display using a cholesteric liquid crystal layer that selectively reflects light of various wavelengths. By controlling voltages applied to display elements, the display device that utilizes such cholesteric liquid crystals can be controlled so that the display device is put into any one of a planar state which reflects light of a specific wavelength, a focal conic state which transmits light, and an intermediate state with a property between the planar state and the focal conic state.
In the display device that utilizes the cholesteric liquid crystals, a display element section (or display panel) in which display elements are disposed in a matrix is driven using a segment driver and a common driver. The segment driver outputs an ON/OFF voltage that corresponds to image data of one line to the display element section, and the common driver outputs an ON/OFF voltage that corresponds to a selected-line position to the display element section. Since the display device that utilizes the cholesteric liquid crystals has the memory function that can maintain a display image, it is necessary to erase a previous display image before rewriting the display image. Since output voltages of the segment driver and the common driver differ between a drawing operation for a display image and an erasing operation for a display image, it is necessary for a voltage supply circuit to supply at least two types of voltages the electrical potentials of which are different from each other to the segment driver and the common driver.
A drawing unit of a display element section that has a simple matrix structure is one line, and the remaining lines form a non-selected region that is not used for drawing. Among drive voltages supplied to the display element section at the time of drawing, drive voltages supplied to a selected line are, for example, ±24 volts (V) or ±12 V, and drive voltages supplied to the non-selected region are, for example, ±6 V. Since the display device that utilizes the cholesteric liquid crystals has a structure in which display elements that are capacitive loads are disposed in a matrix, the drive voltages supplied to the non-selected region are low voltages compared with the drive voltages supplied to the selected line. However, since the non-selected region occupies a considerable amount of the display area of the display element section, the power consumption of the non-selected region is dominant in the power consumption of the display element section. In addition, since a liquid crystal is driven using an alternate-current drive method, polarity inversion is necessary for the drive voltages.
On the other hand, in order to supply, for example, five drive voltages such as 24 V, 18 V, 12 V, 12 V, and 6 V, the voltage supply circuit typically includes a plurality of operational amplifiers that use a power-supply voltage from a common power source. Therefore, even if drive voltages supplied to the non-selected region are, for example, ±6 V, a voltage of 25 V from the common power source that the plurality of operational amplifiers use is used as the power-supply voltage. As a result, drive power used for driving the display element section increases in proportion to the display area of the display element section.
Namely, in a display device of the related art, which has a memory function, the drive power used for driving the display element section increases in proportion to the display area of the display element section, and hence it is difficult to reduce the power consumption of the display device.
An example of the related art is Japanese Unexamined Patent Application Publication No. 2009-251453.
SUMMARYAccording to an aspect of the invention, a driving method of a display device includes: supplying a first drive voltage from a first circuit, which is driven using a first power-supply voltage from a first power source, and a second drive voltage from a second circuit, which is driven using a second power-supply voltage from a second power source that is lower than the first power-supply voltage; causing a driver circuit section that drives a display element to charge, using the second drive voltage, a display element in a non-selected region in a display element section that includes a plurality of display elements; maintaining a voltage of the display element in the non-selected region, using the second drive voltage; charging the display element by firstly inverting a polarity of image data supplied to the display element section, in a time between application of a negative polarity voltage to the display element section and application of a positive polarity voltage to the display element section; and secondly inverting the polarity of the image data firstly inverted.
According to another aspect of the invention, a display device includes: a display element section including display elements disposed in a matrix; a driver circuit section to drive the display element section on a basis of image data and a first drive voltage; a voltage supply circuit including a first circuit, which is driven using a first power-supply voltage from a first power source, and a second power-supply voltage from a second circuit, which is driven using a second power-supply voltage from a second power source that is lower than the first power-supply voltage, and to supply the drive voltage to the driver circuit section; and an inverting circuit section to input the image data to the driver circuit section, the driver circuit section charges, using a second drive voltage from the second circuit, a display element in a non-selected region in the display element section, and maintains a voltage of the display element in the non-selected region, using the second drive voltage; and the inverting circuit section charges the display element for which a polarity of the image data supplied to the display element section is firstly inverted, in a time between application of a negative polarity voltage to the display element section and application of a positive polarity voltage to the display element section, and secondly inverts the polarity of the image data firstly inverted.
The object and advantages of the invention will be realized and attained at least by the elements, features, and combinations particularly pointed out in the claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.
A voltage supply circuit that supplies a plurality of drive voltages to a driver circuit section includes a first circuit, which is driven using a first power-supply voltage from a first power source, and a second circuit, which is driven using a second power-supply voltage from a second power source that is lower than the first power-supply voltage. Charging of a display element (or a pixel) in a non-selected region in a display element section is performed using a first drive voltage from the first circuit, and, after that, a voltage of the display element in the non-selected region is maintained using a second drive voltage from the second circuit. In addition, a driving method is adopted in which charging of the display element for which a polarity of the image data supplied to the display element section is firstly inverted is performed, in a time between application of a negative polarity drive voltage to the display element section and application of a positive polarity drive voltage to the display element section, and the polarity of the image data firstly inverted is secondly inverted.
According to the driving method, positive-polarity electric charge can be applied to the display element in the non-selected region with the negative polarity of an applied voltage being maintained. Therefore, driving of the display element in the non-selected region is performed using the second drive voltage that is driven using the second power-supply voltage that supplies the lower power-supply voltage, and many of the display elements in the display element section are driven using the second drive voltage. Therefore, the power consumption of the display device can be reduced.
Individual embodiments of a driving method and a display device, which are disclosed, will be described with reference to figures, hereinafter.
The display device 1 includes a power source 11, a voltage boost section 12, a multiple voltage generation section 13, a clock generation section 14, a driver control circuit 15, a segment driver 16, a common driver 17, a display element section (or display panel) 18, an inverter circuit 21, and a switch circuit 22. The inverter circuit 21 and the switch circuit 22 form an inverting circuit section. In response to a switching control signal CNT that is input to the switch circuit 22 from the driver control circuit 15 or an external device (not illustrated) such as a host device or the like, the inverting circuit section inputs image data to the segment driver 16 without or with the polarity of the image data being inverted. As described later, the inverting circuit section charges the display element by inverting the polarity of image data supplied to the display element section 18, in a time between application of a negative polarity voltage to the display element section 18 and application of a positive polarity voltage to the display element section 18, and inverts the polarity of the image data again.
The power source 11 outputs, for example, a power-supply voltage ranging from 3 V to 5 V. The voltage boost section 12 includes a regulator such as a DC-DC converter or the like, and boosts the power-supply voltage from the power source 11 to, for example, a voltage ranging from 24 V to 40 V. As the voltage boost section 12 may include a regulator, a typical integrated circuit (IC) can be used. Since such an IC has a function that allows a boosted voltage to be adjusted by setting a feedback voltage, one of a plurality of voltages generated by voltage dividing or the like that uses resistances is selected and fed back to a feedback terminal, thereby allowing the boosted voltage to be varied. The multiple voltage generation section 13 generates various kinds of voltages by resistive-dividing the boosted voltage from the voltage boost section 12, and stabilizes the various kinds of voltages generated. The various kinds of voltages generated by the multiple voltage generation section 13 are supplied as drive voltages to the segment driver 16 and the common driver 17 that form the driver circuit section in the display device 1.
The clock generation section 14 generates a clock that determines operation timing in the display device 1. The driver control circuit 15 generates various kinds of control signals on the basis of the clock and the image data, and supplies the various kinds of control signals to the segment driver 16 and the common driver 17. The driver control circuit 15 is, for example, a microcomputer, a central processing unit (CPU), a field programmable gate array (FPGA)/complex programmable logic device (CPLD) or the like.
The segment driver 16 outputs an ON/OFF voltage that corresponds to image data of one line to the display element section 18, and the common driver 17 outputs an ON/OFF voltage that corresponds to a selected-line position to the display element section 18. For example, the segment driver 16 drives 768 data lines, and the common driver 17 drives 1024 scan lines. Since pieces of data supplied to individual display elements R, G, and B are different from one another, the segment driver 16 separately drives individual data lines. The common driver 17 commonly drives R, G, and B lines. The image data inputted to the segment driver 16 is 4-bit data where, for example, a full-color original image is converted into 4096-color data of 16 tones for each of R, G, and B by an error diffusion method. For this tone conversion, a method by which a high display quality is obtained is desirable, and a blue-noise mask method or the like may be used according to the error diffusion method.
The display element section 18 has, for example, a structure which complies with an A-4 size eXtended Graphics Array (XGA) specification and in which 1024×768 display elements that use cholesteric liquid crystals are disposed in a matrix. The display element section 18 may have a structure that has suitable flexibility in accordance with an intended use, or may have a rigid structure that has no flexibility.
In the embodiment, the driver control circuit 15 outputs image data DATA to be supplied to the segment driver 16, and also outputs, as the various kinds of control signals, a data latch/scan shift signal LPCOM that indicates a scan line to be scanned by the common driver 17, a data capture clock XSCL that controls the transfer timing of the image data, a frame start signal DIO that indicates the start of a display line, a pulse polarity control signal FR that indicates the polarity inversion of voltages supplied to the segment driver 16 and the common driver 17, a data latch/scan shift signal LPSEG that indicates the update of a display line, and a driver output off signal /DSPOF that turns off the voltages supplied to the segment driver 16 and the common driver 17. Using the various kinds of control signals, the segment driver 16 and the common driver 17 cause the display element section 18 to display an image that corresponds to the image data.
In addition, in this example, since the data capture clock XSCL is not used in the common driver 17, it may not be necessary to supply the data capture clock XSCL to the common driver 17. In addition, while the frame start signal DIO is supplied to the common driver 17, a signal that corresponds to the frame start signal DIO, supplied to the segment driver 16, is fixed to a ground GND.
As illustrated in
As illustrated in
Using the segment driver 16 and the common driver 17, the display element section 18 can be scanned with respect to each line.
Next, a relation between the output voltages of the multiple voltage generation section 13 and the output voltages of the segment driver 16 and the common driver 17 will be described with reference to
The individual amplification circuits (GAIN) that form the amplification circuit group 132 includes, for example, an operational amplifier 1320 that has a connection configuration illustrated in
In this example, when an image drawing operation is performed in the display element section 18, output voltages V0=24 V, V21S=12 V, and V34S=12 V are provided for the segment driver 16, and output voltages V0=24 V, V21C=18 V, and V34C=6 V are provided for the common driver 17. In addition, the output voltages of the segment driver 16 meet the following relation: V0≧V21S≧V34S≧V5≧0 V, and the output voltages of the common driver 17 meet the following relation: V0≧V21C≧V34C≧V5≧0 V. Namely, the output voltages of the segment driver 16 and the common driver 17 at the time of drawing meet the following relation: V0≧V21≧V34≧V5≧0 V.
On the other hand, in order to supply, for example, five drive voltages of 24 V, 18 V, 12 V, 12 V, and 6 V, the voltage supply circuit includes a plurality of operational amplifiers 1320 that use the power-supply voltage Vref from the common power source, as illustrated in
The output voltage of the driver illustrated in
Next, another example of the multiple voltage generation section 13 that can reduce the power consumption of the display device 1 will be described.
The amplification circuit 1320 (namely, an operational amplifier) in the amplification circuit section 1311 is driven using a power-supply voltage V1 that has, for example, a voltage of 25 V. On the other hand, the amplification circuit 1320 (namely, an operational amplifier) in the amplification circuit section 1312 is driven using a power-supply voltage V2 that has, for example, a voltage of 13 V. The power-supply voltages V1 and V2 (V1>V2) are supplied from power sources different from each other. The amplification circuit section 1311 outputs drive voltages V0=24 V, V21C=18 V, and V21S=12 V. On the other hand, the amplification circuit section 1312 outputs drive voltages V34S=12 V and V34C=6 V. In this example, there is a potential difference of 6 V between the drive voltages V0, V21C, and V21S, and there is a potential difference of 6 V between the drive voltages V34S and V34C.
In this way, in the multiple voltage generation section 13 in
First, as illustrated in
Next, as illustrated in
Next, as illustrated in
Finally, after a voltage application time during which a voltage has a positive polarity and is normal elapses, a line to be scanned next is selected as the selected line 18L, and the processing operation returns to the first phase Ph1. Afterward, in substantially the same way, every time each selected line 18L is selected, the above-described first phase Ph1 to third phase Ph3 are repeated.
In the embodiment, when the processing operation makes the transition from the first phase Ph1 to the third phase Ph3, the processing operation is routed through the second phase Ph2. In the second phase Ph2, charging of the display elements 18E in the non-selected lines 18U, which is to be performed in the following third phase Ph3, is preliminarily performed. Since the multiple voltage generation section 13 includes the voltage supply circuit that has the above-described configuration, processing operations performed in the first phase Ph1 and the second phase Ph2 is based on a drive voltage output from the amplification circuit (namely, an operational amplifier) 1320 driven using the power-supply voltage V2 from the power source that has the low voltage of 13 V. In addition, a processing operation based on a drive voltage output from the amplification circuit (namely, an operational amplifier) 1320 driven using the power-supply voltage V1 from the power source that has the high voltage of 25 V is performed for the selected line 18L in the third phase Ph3. In this way, a processing operation performed for many of the display elements 18E in the display element section 18 is based on a drive voltage output from the amplification circuit (namely, an operational amplifier) 1320 driven using the power-supply voltage V2 from the power source that has the low voltage. Therefore, the power consumption of the display device 1 can be reduced compared with a driving method of the related art.
In a display device 111 illustrated in
The operational amplifier 1320 (namely, an operational amplifier) in the amplification circuit section 1321 is driven using a power-supply voltage V1 that has, for example, a voltage of 25 V. In addition, the operational amplifier 1320 (namely, an operational amplifier) in the amplification circuit section 1322 is driven using a power-supply voltage V2 that has, for example, a voltage of 13 V. Furthermore, the operational amplifier 1320 (namely, an operational amplifier) in the amplification circuit section 1323 is driven using a power-supply voltage V3 that has, for example, a voltage of 7 V. The power-supply voltages V1, V2, and V3 (V1>V2>V3) are supplied from power sources different from one other. The amplification circuit section 1321 outputs drive voltages V0=24 V, V21C=18 V, and V21S=12 V. The amplification circuit section 1322 outputs a drive voltage V34S=12 V and, the amplification circuit section 1323 outputs a drive voltage V34C=6 V.
In this way, in the multiple voltage generation section 13 in
In addition, it should be understood that if the voltage values of the voltages V0, V21S, V21C, V34S, V34C, and V5 meet the relation described above, the voltage values of the voltages V0, V21S, V21C, V34S, V34C, and V5 are not limited to the voltages cited in the individual embodiments.
All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Although the embodiments in accordance with aspects of the present inventions have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.
Claims
1. A driving method of a display device comprising:
- supplying a first drive voltage from a first circuit, which is driven using a first power-supply voltage from a first power source, and a second drive voltage from a second circuit, which is driven using a second power-supply voltage from a second power source that is lower than the first power-supply voltage;
- causing a driver circuit section that drives a display element to charge, using the second drive voltage, a display element in a non-selected region in a display element section that includes a plurality of display elements;
- maintaining a voltage of the display element in the non-selected region, using the second drive voltage;
- charging the display element by firstly inverting a polarity of image data supplied to the display element section, in a time between application of a negative polarity voltage to the display element section and application of a positive polarity voltage to the display element section; and
- secondly inverting the polarity of the image data firstly inverted.
2. The driving method of the display device according to claim 1, wherein
- the application of the negative polarity voltage is executed before the application of the positive polarity voltage.
3. The driving method of the display device according to claim 2, wherein
- the image data the polarity of which is firstly inverted is being applied to the display element section until charging of the display element in the non-selected region is completed.
4. The driving method of the display device according to claim 2, wherein
- a positive polarity drive voltage is supplied to the driver circuit section when the polarity of the image data firstly inverted is secondly inverted.
5. The driving method of the display device according to claim 2, wherein
- a time of the application of the positive polarity voltage to the display element section performed by the driver circuit section is shorter by a time, which corresponds to a time of supply of the image data firstly inverted to the display element section, than a time of the application of the negative polarity voltage.
6. A display device comprising:
- a display element section including display elements disposed in a matrix;
- a driver circuit section to drive the display element section on a basis of image data and a first drive voltage;
- a voltage supply circuit including a first circuit, which is driven using a first power-supply voltage from a first power source, and a second circuit, which is driven using a second power-supply voltage from a second power source that is lower than the first power-supply voltage, and to supply the first drive voltage to the driver circuit section; and
- an inverting circuit section to input the image data to the driver circuit section,
- the driver circuit section charges, using a second drive voltage from the second circuit, a display element in a non-selected region in the display element section, and maintains a voltage of the display element in the non-selected region, using the second drive voltage; and
- the inverting circuit section charges the display element for which a polarity of the image data supplied to the display element section is firstly inverted, in a time between application of a negative polarity voltage to the display element section and application of a positive polarity voltage to the display element section, and secondly inverts the polarity of the image data firstly inverted.
7. The display device according to claim 6, wherein
- the voltage supply circuit supplies the drive voltage to the driver circuit section so that the application of the negative polarity voltage is executed before the application of the positive polarity voltage.
8. The display device according to claim 7, wherein
- the inverting circuit section is applying the image data the polarity of which is firstly inverted to the display element section until charging of the display element in the non-selected region is completed.
9. The display device according to claim 7, wherein
- the voltage supply circuit supplies a positive polarity drive voltage to the driver circuit section when the inverting circuit section secondly inverts the polarity of the image data firstly inverted.
10. The display device according to claim 7, wherein
- a time of the application of the positive polarity drive voltage to the display element section performed by the driver circuit section is shorter by a time, which corresponds to a time of supply of the image data firstly inverted to the display element section, than a time of the application of the negative polarity drive voltage.
11. The display device according to claim 6, wherein
- the display element section includes a cholesteric liquid crystal.
Type: Application
Filed: Dec 13, 2010
Publication Date: Jun 23, 2011
Applicant: FUJITSU LIMITED (KAWASAKI-SHI)
Inventor: Hirokata UEHARA (Kawasaki)
Application Number: 12/966,188